Work machines such as, for example, excavators, dozers, loaders, motor graders, and other types of heavy machinery typically use one or more hydraulic actuators to accomplish a variety of tasks. The actuators are fluidly connected to one or more pumps that provide pressurized fluid to chambers within the actuators. An electro-hydraulic valve arrangement is typically connected between the pumps and the actuators to control a flow rate and direction of pressurized fluid to and from the chambers of the actuators.
The electro-hydraulic valve arrangements often include either single-valve or multi-valve arrangements. Single valve arrangements typically include a valve having only two positions with fixed flow areas to direct flow into and out of the chambers. Single-valve arrangements may also include a bypass orifice which directs fluid flow from the pump to a reservoir which may provide a desired feedback to an operator. Operator feedback may occur during a resistive movement of the actuator, such as when the load on the actuator increases, e.g., when a work implement transitions from soft soil to hard soil. A resistive movement of the actuator increases the pressure within the hydraulic system which causes an increase in fluid flow through the bypass orifice to the reservoir. As such, an operator may sense a slower movement of the actuator and/or a machine component, may sense the need to further actuate a control lever to move an associated component, may sense an engine surge to increase the supply of fluid to the hydraulic system, and/or may sense a variety of other operational changes.
Multi-valve arrangements provide increased flexibility over single-valve arrangements by allowing independent control of fluid into and out of each chamber of an actuator. Multi-valve arrangements may not, however, include bypass orifices and thus may adversely affect feedback to an operator during work machine operation.
Additionally, the pumps that may supply fluid to the actuators often require a continuous flow of fluid therethrough to maintain lubrication and cooling of the pump. Furthermore, in multi-pump systems, some actuators may only require pressured fluid from one pump, while other actuators may require pressurized fluid from more than one pump. Accordingly, unnecessary fluid flow may be supplied within portions of a hydraulic system, resulting in unwanted pressure increases, and/or wasted energy.
U.S. Pat. No. 5,540,049 (“the '049 patent”) issued to Lunzman discloses a control system and method for a hydraulic actuator. The '049 patent includes a hydraulic system having a variable flow hydraulic pump delivering fluid under pressure to the hydraulic actuator. The '049 patent also includes a closed center valve that operates to control a flow of the hydraulic fluid to the hydraulic actuator and a separate bypass valve that operates to control a flow of the hydraulic fluid to a fluid reservoir. A control system, having a separate bypass controller that calculates the effect of a closed center valve stroke signal, responsively controls the separate bypass valve. The separate bypass controller calculates the effect of the closed center valve stroke signal and derives a signal based on pressure modulation to control the separate bypass valve.
Although the '049 patent may include a separate bypass valve to control the flow of pressurized fluid to a reservoir, it may bypass flow that is required by the actuator which may undesirably lower the movement speed of the hydraulic actuator. Additionally, the '049 may require a complex pump and valve control system.
The present disclosure is directed to overcoming one or more of the problems set forth above.